Known arts are related to a metal graphite brush, especially the known arts are related to improvement of a life of the metal graphite brush. A first known art disclosed in Japanese Patent No.2641695 relates to a production method of a metal graphite brush, especially, a production method of a metal graphite brush using a specific graphite bond at a specific amount to enhance a binding strength of the metal graphite and decrease a friction coefficient of the metal graphite.
In the first known art, the bond of the brush is prepared by mixing novolak type phenol resin with furfural resin at a specific ratio. Such bond is mixed with the metal graphite and calcinated, and the bond evenly included in the metal graphite is carbonized to become non-crystalloid carbon (generally known as soot). On this account, binding strength between each graphite particle can be improved, which has the same effect as abrasion proof material for adjusting a film on the surface of the brush. Using such material, the film having lubricating property reduces friction resistance of the brush, as a result, abrasion life of the brush can be extended.
A second known art disclosed in Japanese patent Laid-open Publication No. H05(1993)-144534 is also relates to a production method of the metal graphite brush, wherein copper powders of the brush include microparticles and large particles at a certain compounding ratio for reducing the wear of the brush by preventing sliding noise of the brush sliding on a commutator and heat generated by the friction.
Specifically, in the second know art, the copper powder having a large particle diameter reduces a contact resistance of the brush against the commutator. As a result, the heating value is reduced, and the abrasion life is improved.
As aforementioned above, each known art uses different means for improving the abrasion life of the brush. Specifically, the first known art uses the film having lubricating property, which is made by applying and calcinating the mixture of the novolak type phenol resin and the furfural resin. In the second known art, on the other hand, the brush includes two different kinds of copper powders having different diameter for reducing the contact resistance between the copper powder having large particle diameter and the commutator.